This invention relates to a lubrication system for an internal combustion engine and more particularly to a dry sump lubrication system including a non-vented oil tank which is located externally of the engine crankcase.
Dry sump lubrication systems are commonly used with high performance engines such as engines used in race cars or aircraft. In such dry sump lubrication systems a supply of lubricating oil is kept in a reservoir or tank which is separate from the sump portion of the crankcase of the engine and which is generally located externally of the engine. During operation of the engine oil is pumped from this tank and is fed directly to the bearings and other parts of the engine which are to be lubricated. The oil which is thrown from the crankshaft and bearings during the operation of the engine is received in a sump located in a lower part of the crankcase from whence the oil is pumped back to the tank by means of a separate pump. However, the lubricating oil which is pumped from the sump contains a large quantity of air, which has been absorbed into the oil due to splashing of the oil during the lubricating process. Furthermore, air is also absorbed into the oil as the oil is pumped from the sump by the scavenger pump. This absorbed air in the lubricating oil results in lowered lubricating efficiency of the oil, thereby causing undesirable heating of the engine and loss of engine efficiency. Furthermore, the lower lubricating efficiency of the oil increases the wear of the engine and therefore lowers the life of the various engine parts.
Various solutions to this problem have been offered by the prior art dry sump lubricating systems. Thus, for instance, in some engines castor oil has been used as a lubricant, since the foaming property of castor oil is superior to that of mineral oil.
Another solution which has been offered is disclosed in U.S. Pat. No. 2,538,983. In this patent a separate deaerator is provided for deaerating the oil after it is pumped from the engine sump by the scavenger pump and before the oil is returned to the engine. The deaerater consists of a cylindrical tank in which the oil is sprayed tangentially against the inside surface of the tank wall. Some of the entrained air is thereby separated from the oil by centrifugal force due to the rotating movement of the oil during passage of the oil along the inside surface of the cylindrical wall from the inlet to the outlet of the deaerator. This type of air separator is relatively inefficient and does not remove sufficient quantities of air. Another problem with this type of air separator is its complexity. It is therefore desired to provide a dry sump lubrication system wherein an effective and simple air separator is provided.
In prior art dry sump lubrication systems the engine and oil tank are generally vented to the atmosphere whereby the engine operates at substantially atmospheric pressure. By operating the engine at atmospheric pressure, increased friction will result in the engine thereby causing lower efficiency of the engine. It is therefore desired to provide a dry sump lubrication system including a non-vented oil tank which communicates with the engine whereby the engine and oil tank are operated at below atmospheric pressure.
U.S. Pat. No. 2,888,097, discloses a dry sump lubrication system for aircraft engine wherein a separate deaerating pump is provided for deaerating the oil as it leaves the scavenger pump. This patent also discloses two stages of scavenger pumps and furthermore discloses a lubricant pump for returning deaerated lubricant to the engine. In this system oil is removed and directly returned to engine 10, while a separate oil tank is used only as an overflow tank. Furthermore, in this lubrication system the air which is separated from the oil is fed to a gear casing which houses the gears for driving the lubricant pump, the deaerating pump, and the scavenger pump. The gear casing is vented to the atmosphere. Since this engine does not appear to be provided with a pressure relief, pressures may build up in the engine which can cause failure of gaskets and burning up of the engine. An additional problem with this structure is that any oil which is entrained in the air entering the gear casing, and which condenses out in the gear casing, will tend to fill up the gear casing and will overflow through the vent out of the engine. This is of course unsatisfactory, particularly in race cars.
It is therefore desired to provide a dry sump lubrication system wherein any oil which condenses out of the separated oil may be returned to the engine, wherein the engine and oil tank are operated at sub-atmospheric pressure and wherein the nonvented oil tank is provided with a pressure relief valve.